The need to remain cost and performance competitive in the production of semiconductor devices has caused continually increasing device density in integrated circuits. To facilitate the increase in device density, new technologies are constantly needed to allow the feature size of these semiconductor devices to be reduced. High device density also requires low-power operation.
The push for ever increasing device densities is particularly strong in CMOS technologies, such as in the design and fabrication of field effect transistors (FETs). FETs are used in almost all types of integrated circuit design (i.e., microprocessors, memory, etc.). Fin-type field effect transistors (FinFETs) are low-power, high speed, vertically scaled transistors that can be densely packed on a chip. Vertical scaling involves creating a thin wall of semiconductor (the “fin”) and creating the FET on the side of the wall. Thin typically refers to widths that are less than minimum lithographic dimension.
Unfortunately, FinFETs are not suitable for all purposes. Different applications require different transistor device behaviors. Thin devices such as FinFETs reach full depletion during operation. This is desirable for many applications. Different behavior is required for other applications. Thick-body devices behave differently because they do not reach full depletion.
Some applications could benefit from having FinFETs and thick-body devices on the same chip. This has been difficult to achieve economically because the manufacturing steps for FinFETs and thick-body devices are different. Currently, one entire set of masks must be created and the associated steps taken for FinFETs and then another entire set of masks created and steps taken for thick-body devices. The masks protect thin technology devices while forming thick-technology devices, or vice versa. The use of a great multiplicity of masks and steps is expensive. Thus, there is a need for improved methods of fabrication of integrated circuits that use both FinFETs and thick-body devices on the same chip.